Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

1. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

Four heat exchangers

One heat exchanger

2. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

At critical Temperature

3. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Low boiling point

Large latent heat

High risibility with oil

4. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

5. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

6. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

7. The boiling point of ammonia is

-77.7°C

-30°C

-33.3°C

-10.5°C

8. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

9. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

10. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

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11. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

12. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Negative

Positive

13. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Any one of the above

Always more than unity

Always less than unity

14. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 9

1: 3

1: 1

15. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

16. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Water coolers

Room air conditioners

17. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Rankine

Reversed Carnot

18. Rating of a domestic refrigerator is of the order of

0.1 ton

10 tons

5 tons

40 tons

19. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

20. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

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21. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

22. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

23. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

4.33

3.33

1.33

24. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

25. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Axial

Centrifugal

Miniature sealed unit

26. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

Absorber

27. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-77.7°C

-135.8°C

28. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

29. Most thermostatic expansion valves are set for a superheat of

20°C

15°C

10°C

5°C

30. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Page 4 of 4

31. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Sub-cooling or under-cooling

Normal cooling

32. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.4

0.376

0.67

33. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

34. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

35. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

36. Which of the following cycles uses air as the refrigerant?

Stirling

Ericson

Bell Coleman

Carnot

37. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

38. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

8 bar

2 bar

39. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Brine

Carbon dioxide

Freon

40. For obtaining high COP, the pressure range of compressor should be

High

Any value

Optimum

Low

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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